1. Field of Invention
The present invention relates to a method of fabricating insulating films for application in thin film transistors (TFTs) and metal insulator semiconductor (MIS) transistors.
2. Description of Related Art
Forming an insulating film, such as SiO2, constitutes one of the significant steps in the manufacture of transistors, such as silicon MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Formation of SiO2 film on silicon is performed at temperatures that typically exceed 1000xc2x0 C. in the presence of chemical species that oxidize the silicon. This process is known as thermal oxidation.
The thermal oxidation process is subject to undesirable side-effects, such as redistribution of the dopant profiles in the semiconductors, since significant diffusion of dopants occurs at the high temperatures that are effected in this process. An oxidation temperature that is below 700xc2x0 C. is desirable to suppress these side-effects.
Thin film transistor (TFT) devices, which have a basic structure similar to that of a typical MOSFET, have been used for display applications, such as liquid crystal displays (LCD) and organic electroluminescence displays (OELD). Such devices require a SiO2 layer to be formed at a temperature which is below 430xc2x0 C., since these displays use optically transparent substrates, such as glass, which cannot withstand higher temperatures. For such TFT-applications, deposited SiO2 films are currently used, which are of inferior quality and also form an inferior interface with silicon as compared to SiO2 which is produced by oxidation of silicon; thereby adversely affecting the TFT performance. Thus, the oxidation process must be performed at temperatures that are as low as possible.
The object of the present invention is to provide an inexpensive and simple method for fabricating high quality insulating films at low temperatures.
In accordance with the invention, high quality SiO2 films are fabricated on silicon by supplying photon energy to a mixture of noble gas and oxidizing gas (such as O2, H2O, N2O) to create reactive oxygen, which reacts with silicon to form SiO2.
The invention also covers a similar process that can also be also used to form silicon nitride film by supplying photon energy to a mixture of noble gas and nitriding gas (such as NH3, N2 etc.).
These methods, wherein the energy is supplied to the gas mixtures using photons, are advantageous because they are simple and inexpensive. Instead of photon energy, other energy sources, such as ion beams or electron beams, can also be used.